Many computer architectures implement some form of hierarchical protection domains or “rings.” Each protection ring has an associated privilege mode (i.e., from a high-privilege mode to a low-privilege mode). The operating system of a computing device, for example, is generally executed in the highest-privileged mode. In software vernacular, the protection ring with the highest privilege is often referred to as “Ring 0” or kernel-mode, with lower privilege rings being assigned increasing numbers (e.g. Ring 1, Ring 2, Ring 3, etc.). Although a particular computer architecture or operating system may utilize any number of protection rings, some computer architectures or operating systems utilize a reduced protection ring scheme having only a few protection rings (e.g. only Ring 0 and Ring 3). The use of protection domains or rings allow the corresponding computer system to provide protection of data and applications executed in each protection ring from those executed in other protection rings. For example, in some computer systems, cross ring accesses (e.g. a Ring 0-to-Ring 3 access) may be restricted or even prohibited.
Device drivers are software programs that control a particular device of a computing system. Device drivers act as an interface between an operating system of the computing system, or application executed by the operating system, and the corresponding hardware device. In many computing systems, device drivers are executed in a high-privileged protection ring such as Ring 0, along with the operating system. Software applications, on the other hand, are executed in a lower privileged ring, such as Ring 3. Many legitimate device drivers perform cross ring accesses (e.g. a Ring 0-to-Ring 3 access) during execution. Some operating systems facilitate the cross ring accesses by providing a specific application interface program (API), which must be used by the device drive to perform the cross ring access without causing a violation. However, many device drivers may not implement such APIs or otherwise be configured to perform the cross ring accesses in a secure manner. As such, to function properly, computer systems generally must allow all device drivers to run without any cross ring access protection or globally enforce cross ring access protection, which causes legacy device drivers to stop functioning properly. As such, the ability to provide cross ring access protection for memory accesses from a higher protection ring to a lower protection ring in a typical computer system using various device devices is limited.